A number of tasks, such as ball localization in a football, or soccer, match, presuppose knowledge of the position and/or orientation of objects. In football matches, one of the most controversial topics is whether or not in critical situations the ball has crossed the goal line. To this end, it is necessary that the position of the ball at the goal line may be measured with an accuracy of approximately +/−1.5 cm. Also, it is necessary for any influences exerted by persons who are moving close to the ball and/or are covering the ball to be irrelevant.
There are numerous localization methods based, for example, on optical 2D or 3D sensors having an evaluation system, on exploitation of the known radar principle or of a principle of radio localization.
A principle of radio localization is the localization of objects by means of electromagnetic wave propagation. In this context, a receiver is integrated into an object to be localized, or is attached to an object to be localized, the receiver transmitting data to a central transceiver upon request. A position of the object may thereafter be calculated from signal traveling times and/or from differences between at least two signals received at different antennas.
Radio localization of objects may be performed, for example, by means of the so-called RFID technology (RFID=radio frequency identification). For spatial resolution methods, wherein a relatively precise position of an RFID transponder is to be determined in space, battery-powered, i.e. active, RFID transponders are most often used. A disadvantage of radio localization consists in a shadowing and/or a reflection of electromagnetic waves by certain obstacles, for example. As a result, systems based on radio localization will not achieve the accuracy called for making goal decisions in football, or soccer, for example.
As has already been described, current localization methods are based, for example, on optical 2D or 3D sensors comprising an evaluation system, or they are based on the use of battery-powered, i.e. active, RFID transponders. Such localization methods entail high investment and maintenance cost, sensitivity toward environmental conditions and a high effort called for adapting the evaluation algorithms. Systems exploiting radio localization are not suitable for local-area localization, i.e for determining the positions of objects within a small area, since with a small geometric expansion, differences of different signal traveling times can hardly be measured. Thus, the requirements placed upon systems for localizing objects are not met, or are met only to an insufficient degree, by these methods with regard to economic efficiency, robustness, clock time and independence of an object for exactly determining a position, for example, within a range of a few centimeters.